Sol-gel chemistry provides a low temperature route for preparing metal and certain non-metal oxides that are the prevalent materials used in nanoscience and nanotechnology, as well as in biological systems. C. J. Brinker et al., Sol-gel science: the physics and chemistry of sol-gel processing, Academic Press, Boston, 1990. For example, low reactivity, high temperature stability, biocompatibility, tuneable architecture, and ease of synthesis have made silica (SiO2) a prevalent material for end applications, such as catalysis, photonics, and responsive materials. W. Stöber, et al., J. of Colloid and Interface Science 1968, 26, 62. Metal and non-metal oxides such as silica are relatively inert, however, and other types of functionalities must be combined with the silica for use of these hybrids in applications such as catalysis and sensing.
Since the advent of sol-gel chemistry, a primary goal has been to introduce functionality to these relatively inert substrates. To that end, numerous methods to combine substrates with metals, as well as organometallic, organic, and biological molecules have been developed. These functional particles can be added before, during, or after the sol-to-gel transition. However, if the functional species is added before the sol-to-gel transition, it must be compatible with the sol-gel process. Common routes involve the simultaneous hydrolysis and condensation of a multifunctional single-source precursor or several compatible precursors. K. W. Terry et al., J. of the Am. Chem. Soc. 1997, 119, 9745; P. T. Tanev et al., Nature 1994, 368, 321. Achieving similar rates of hydrolysis and condensation is difficult, however, and these routes have not been generalized. Adding the functional species during the sol-to-gel transition can achieve high loadings, but this method limits the architectures to monoliths. C. A. Morris et al., Science 1999, 284, 622. Moreover, although almost any type of species can be added after the sol-to-gel transition via surface functionalization, the loading of the functional species is limited and the process can impede access to micro or mesopores.
Using single-source precursors—that is, adding functionality before the sol-to-gel transition—is, in principle, the easiest way to incorporate functionality while maintaining access to numerous architectures. The simplest method involves adding water and possibly a solvent to the precursor and allowing the sol-gel process to take its course. Numerous precursors, especially those with lanthanides bound via a linker to a silicon alkoxide, have been developed for fluorescence studies C. Sanchez et al., Adv. Materials 2003, 15, 1969. Synthesizing these single source precursors require complex, multistep syntheses, however. P. Lenaerts, et al., Chemistry of Materials 2005, 17, 5194.
Moreover, while a given route may enable incorporation of a particular metal, the method may not be applicable or extendable to many other metals, or materials. Furthermore, existing methods have been unsuccessful in incorporating biological molecules such as amino acids, peptides and proteins, while claiming success in covalently binding only such biological compounds as saccharides to metal oxides (Brennan et al, Ultrasensitive ATP Detection Using Firefly Luciferase Entrapped in Sugar Modified Sol-gel-Derived Silica, JACS, 2004). Existing methods also prevent the simultaneous incorporation of metals and bioorganic molecules. Accordingly, there is a need for a single source, generalizable method to allow the direct incorporation of metals and other materials in the sol-gel process at higher loading levels, a need that the invention disclosed herein satisfies.